The present invention is directed to crosslinked fluoropolymer materials. More specifically, the present invention is directed to crosslinked fluoropolymer materials suitable for applications such as fuser member coatings for imaging processes and the like. One embodiment of the present invention is directed to a fuser member comprising a substrate and at least one layer thereover, said layer comprising a crosslinked product of a composition which comprises (a) a fluoroelastomer, and (b) an epoxy silane curative.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which can be the photosensitive member itself, or some other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. To fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner to be bonded firmly to the support.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of from about 90xc2x0 C. to about 200xc2x0 C. or higher, depending on the softening range of the particular resin used in the toner. It may be undesirable, however, to increase the temperature of the substrate substantially higher than about 250xc2x0 C. because of the tendency of the substrate to discolor or convert into fire at such elevated temperatures, particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat can be applied by heating one or both of the rolls, plate members, or belt members. Fusing of the toner particles occurs when the proper combination of heat, pressure, and/or contact for the optimum time period are provided. The balancing of these variables to bring about the fusing of the toner particles is well known in the art, and can be adjusted to suit particular machines or process conditions.
During the operation of one fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between a pair of rolls, plates, belts, or combination thereof. The concurrent transfer of heat and the application of pressure in the nip effects the fusing of the toner image onto the support. It is important in the fusing process that minimal or no offset of the toner particles from the support to the fuser member takes place during normal operations. Toner particles offset onto the fuser member can subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thereby increasing the image background, causing inadequate copy quality, causing inferior marks on the copy, or otherwise interfering with the material being copied there as well as causing toner contamination of other parts of the machine. The referred to xe2x80x9chot offsetxe2x80x9d occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release properties of the fuser member, and accordingly it is desirable to provide a fusing surface having a low surface energy to provide the necessary release.
To ensure and maintain good release properties of the fuser member, it has become customary to apply release agents to the fuser member during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils, such as polydimethyl siloxane, or substituted silicone oils, such as amino-substituted oils, mercapto-substituted oils, or the like, to prevent toner offset. In addition, fillers can be added to the outer layers of fuser members to increase the bonding of the fuser oil to the surface of the fuser member, thereby imparting improved release properties.
The use of polymeric release agents having functional groups which interact with a fuser member to form a thermally stable, renewable self-cleaning layer having good release properties for electroscopic thermoplastic resin toners, is described in, for example, U.S. Pat. Nos. 4,029,827, 4,101,686, and 4,185,140, the disclosures of each of which are totally incorporated herein by reference. Disclosed in U.S. Pat. No. 4,029,827 is the use of polyorganosiloxanes having mercapto functionality as release agents. U.S. Pat. Nos. 4,101,686 and 4,185,140 are directed to polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether, and mercapto groups as release fluids.
It is important to select the correct combination of fuser surface material, any filler incorporated or contained therein, and fuser oil. Specifically, it is important that the outer layer of the fuser member react sufficiently with the selected fuser oil to obtain sufficient release. To improve the bonding of fuser oils with the outer surface of the fuser member, fillers have been incorporated into or added to the outer surface layer of the fuser members. The use of a filler can aid in decreasing the amount of fusing oil necessary by promoting sufficient bonding of the fuser oil to the outer surface layer of the fusing member. It is important, however, that the filler not degrade the physical properties of the outer layer of the fuser member, and it is also important that the filler not cause too much of an increase in the surface energy of the outer layer.
Fillers are also sometimes added to the outer layers of fuser members to increase the thermal conductivity thereof. Examples of such fillers include conductive carbon, carbon black, graphite, aluminum oxide, titanium, and the like, as well as mixtures thereof. Efforts have been made to decrease the use of energy by providing a fuser member which has excellent thermal conductivity, thereby reducing the temperature needed to promote fusion of toner to paper. This increase in thermal conductivity also allows for increased speed of the fusing process by reducing the amount of time needed to heat the fuser member sufficiently to promote fusing. Efforts have also been made to increase the toughness of the fuser member layers to increase abrasion resistance and, accordingly, the life of the fuser member.
With regard to known fuser coatings, silicone rubber has been the preferred outer layer for fuser members in electrostatographic machines. Silicone rubbers interact well with various types of fuser release agents. Fluorocarbon polymers such as perfluoroalkoxypolytetrafluoroethylene (PFA Teflon(copyright)), however, which is frequently used as an outer coating for fuser members, is more durable and abrasion resistant than silicone rubber coatings. Also, the surface energy for PFA Teflon(copyright) is lower than that of silicone rubber coatings.
U.S. Pat. No. 4,257,699 (Lentz), the disclosure of which is totally incorporated herein by reference, discloses a fuser member, fuser assembly, and method of fusing or fixing thermoplastic resin powder images to a substrate in a fuser assembly of the type wherein a polymeric release agent having functional groups is applied to the surface of the fuser member. The fuser member comprises a base member having at least two layers of elastomer thereon, at least the outer layer elastomer surface having a metal-containing filler therein. Exemplary of such a fuser member is an aluminum base member coated with a first layer of poly(vinylidene fluoride-hexafluoropropylene) copolymer optionally having a metal-containing filler, such as lead oxide, dispersed therein, and at least a second layer of poly(vinylidene fluoride-hexafluoropropylene) copolymer having metal-containing filler, such as lead oxide, dispersed therein, coated upon the first layer.
U.S. Pat. No. 4,339,553 (Yoshimura et al.), the disclosure of which is totally incorporated herein by reference, discloses a water-based fluoroelastomer coating composition improved in adhesiveness onto a substrate, which comprises (A) an aqueous fluoroelastomer dispersion blended with (B) an aminosilane compound of the formula 
wherein R is methyl or ethyl, X is a single bond, 
or
"Parenopenst"C2H4xe2x80x94NHxe2x80x94C2H4xe2x80x94NH"Parenclosest"
and y is an integer of 2 or 3 and optionally with (C) an amine compound having at least one terminal amino group directly bonded to an aliphatic hydrocarbon residue.
U.S. Pat. No. 5,017,432 (Eddy et al.), the disclosure of which is totally incorporated herein by reference, discloses a fuser member and fuser system of a type wherein a polymeric release agent having functional groups supplied to the surface of the fuser member has an elastomer fusing surface comprising poly(vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene), wherein the vinylidene fluoride is present in an amount less than 40 mole percent, a metal oxide is present in amounts sufficient to interact with the polymer release agent having functional groups to provide an interfacial barrier layer between the fusing surface and the toner and being substantially unreactive with the elastomer, and wherein the elastomer is cured from a solvent solution thereof with a nucleophilic curing agent soluble in the solution and in the presence of less than 4 parts by weight of inorganic base per 100 parts by weight of polymer, with the inorganic base being effective at least partially to dehydrofluorinate the vinylidene fluoride.
U.S. Pat. No. 5,166,031 (Badesha et al.), the disclosure of which is totally incorporated herein by reference, discloses a fuser member comprising a supporting substrate having an outer layer of a volume grafted elastomer which is a substantially uniform integral interpenetrating network of a hybrid composition of a fluoroelastomer and a polyorganosiloxane, the volume graft having been formed by dehydrofluorination of the fluoroelastomer by a nucleophilic dehydrofluorinating agent, followed by addition polymerization by the addition of an alkene or alkyne functionally terminated polyorganosiloxane and a polymerization initiator.
U.S. Pat. No. 5,337,129 (Badesha), the disclosure of which is totally incorporated herein by reference, discloses an intermediate toner transfer component comprising a substrate and a coating comprising integral, interpenetrating networks of haloelastomer, silicon oxide, and optionally polyorganosiloxane.
U.S. Pat. No. 5,366,772 (Badesha et al.), the disclosure of which is totally incorporated herein by reference, discloses a fuser member comprising a supporting substrate and an outer layer comprising an integral interpenetrating hybrid polymeric network which comprises a haloelastomer, a coupling agent, a functional polyorganosiloxane, and a crosslinking agent.
U.S. Pat. No. 5,370,931 (Fratangelo et al.), the disclosure of which is totally incorporated herein by reference, discloses a fuser member which comprises a supporting substrate comprising an outer layer of a volume grafted elastomer which is a substantially uniform integral interpenetrating network of a hybrid composition of a fluoroelastomer and a polyorganosiloxane, the volume graft having been formed by dehydrofluorination of the fluoroelastomer by a nucleophilic dehydrofluorinating agent, followed by addition polymerization by the addition of an alkene or alkyne functionally terminated polyorganosiloxane and a polymerization initiator, wherein the outer layer contains a reactive metal oxide in an amount of from about 2 to about 7 weight percent.
U.S. Pat. No. 5,456,987 (Badesha), the disclosure of which is totally incorporated herein by reference, discloses an intermediate toner transfer component comprising a substrate and a coating comprising integral, interpenetrating networks of haloelastomer, titanium oxide, and optionally polyorganosiloxane.
U.S. Pat. No. 5,736,250 (Heeks et al.), the disclosure of which is totally incorporated herein by reference, discloses crosslinked fluorocarbon elastomer surfaces comprising a fluorocarbon elastomer and an amino siloxane, and also discloses a method for providing a crosslinked fluorocarbon elastomer surface on a fuser member supporting substrate which includes mixing together an acid acceptor, an emulsifier, water, and amino siloxane with a latex fluorocarbon elastomer.
Copending application U.S. Ser. No. 09/416,149, filed concurrently herewith, entitled xe2x80x9cFuser Member Coating Composition and Processes for Providing Elastomeric Surfaces Thereon,xe2x80x9d with the named inventors Santokh S. Badesha, Clifford O. Eddy, David J. Gervasi, George J. Heeks, and Arnold W. Henry, the disclosure of which is totally incorporated herein by reference, discloses fuser members and processes for fluorocarbon elastomer surfaces containing a fluorocarbon elastomer and a non-amino crosslinker together with methods for providing a crosslinked fluorocarbon elastomer surface on a fuser member supporting substrate which include mixing together an acid acceptor, an emulsifier, water, and a non-amino based crosslinker with a latex fluorocarbon elastomer.
Fluorocarbon elastormers, including those commercially available as, for example, VITON(copyright), ALFAS(copyright), FLUOREL(copyright), TECHNOFLON(copyright), DYNAMINE(copyright), and the like, are used for a number of applications, including layers in fuser members, and are generally prepared from a variety of copolymers containing monomers such as vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, perfluoro(methyl vinyl ether), ethylene, propylene, and the like. Some commercially available compositions are copolymers of these monomers, and contain small amounts of a bromine terminated olefin as a cure site monomer. These polymers are curable with dinucleophiles or peroxides. For example, VITON(copyright) GF, a common overcoat material for fuser members, can be cured with a bisphenol AF based curative (VC-50, available from E. I. DuPont de Nemours and Co). Present processes for fabrication of fuser coatings and other coatings containing fluoroelastomers generally contain a ball-milling step. The purpose of this ball-milling step is to reduce the particle size of the basic metal oxides often used for standard curing systems. In some situations, the particle size of these oxides may be insufficiently reduced to achieve a uniform coating free of surface defects.
Accordingly, while known compositions and processes are suitable for their intended purposes, a need remains for improved crosslinked fluoroelastomer materials. In addition, a need remains for improved methods for curing fluoroelastomer materials. Further, a need remains for methods for curing fluoroelastomers in the absence of particulate basic metal oxides. Additionally, a need remains for methods for curing fluoroelastomers that can employ lower curing temperatures than those presently used. There is also a need for crosslinked fluoroelastomer materials that have desirably high levels of heat stability. In addition, there is a need for crosslinked fluoroelastomer materials that have improved toughness characteristics. Further, there is a need for simplified methods for curing fluoroelastomers. Additionally, there is a need for crosslinked fluoroelastomer materials that need no additional adhesive when they are bound to surfaces such as silicones or other fluoroelastomers. A need also remains for crosslinked fluoroelastomer materials having pigment particles (such as those used to enhance electrical or thermal conductivity) well and uniformly dispersed therein.
The present invention is directed to a fuser member comprising a substrate and at least one layer thereover, said layer comprising a crosslinked product of a composition which comprises (a) a fluoroelastomer, and (b) an epoxy silane curative.